// Package dca 即Domestic cryptographic algorithm
// 该库封装了一系列的国产密码算法
package dca

import (
	"encoding/hex"
)

// 系统参数
var FK = [4]uint32{0xA3B1BAC6, 0x56AA3350, 0x677D9197, 0xB27022DC}

var CK = [32]uint32{
	0x00070e15, 0x1c232a31, 0x383f464d, 0x545b6269,
	0x70777e85, 0x8c939aa1, 0xa8afb6bd, 0xc4cbd2d9,
	0xe0e7eef5, 0xfc030a11, 0x181f262d, 0x343b4249,
	0x50575e65, 0x6c737a81, 0x888f969d, 0xa4abb2b9,
	0xc0c7ced5, 0xdce3eaf1, 0xf8ff060d, 0x141b2229,
	0x30373e45, 0x4c535a61, 0x686f767d, 0x848b9299,
	0xa0a7aeb5, 0xbcc3cad1, 0xd8dfe6ed, 0xf4fb0209,
	0x10171e25, 0x2c333a41, 0x484f565d, 0x646b7279,
}

var SboxSm4 = [16][16]uint32{
	{0xd6, 0x90, 0xe9, 0xfe, 0xcc, 0xe1, 0x3d, 0xb7, 0x16, 0xb6, 0x14, 0xc2, 0x28, 0xfb, 0x2c, 0x05},
	{0x2b, 0x67, 0x9a, 0x76, 0x2a, 0xbe, 0x04, 0xc3, 0xaa, 0x44, 0x13, 0x26, 0x49, 0x86, 0x06, 0x99},
	{0x9c, 0x42, 0x50, 0xf4, 0x91, 0xef, 0x98, 0x7a, 0x33, 0x54, 0x0b, 0x43, 0xed, 0xcf, 0xac, 0x62},
	{0xe4, 0xb3, 0x1c, 0xa9, 0xc9, 0x08, 0xe8, 0x95, 0x80, 0xdf, 0x94, 0xfa, 0x75, 0x8f, 0x3f, 0xa6},
	{0x47, 0x07, 0xa7, 0xfc, 0xf3, 0x73, 0x17, 0xba, 0x83, 0x59, 0x3c, 0x19, 0xe6, 0x85, 0x4f, 0xa8},
	{0x68, 0x6b, 0x81, 0xb2, 0x71, 0x64, 0xda, 0x8b, 0xf8, 0xeb, 0x0f, 0x4b, 0x70, 0x56, 0x9d, 0x35},
	{0x1e, 0x24, 0x0e, 0x5e, 0x63, 0x58, 0xd1, 0xa2, 0x25, 0x22, 0x7c, 0x3b, 0x01, 0x21, 0x78, 0x87},
	{0xd4, 0x00, 0x46, 0x57, 0x9f, 0xd3, 0x27, 0x52, 0x4c, 0x36, 0x02, 0xe7, 0xa0, 0xc4, 0xc8, 0x9e},
	{0xea, 0xbf, 0x8a, 0xd2, 0x40, 0xc7, 0x38, 0xb5, 0xa3, 0xf7, 0xf2, 0xce, 0xf9, 0x61, 0x15, 0xa1},
	{0xe0, 0xae, 0x5d, 0xa4, 0x9b, 0x34, 0x1a, 0x55, 0xad, 0x93, 0x32, 0x30, 0xf5, 0x8c, 0xb1, 0xe3},
	{0x1d, 0xf6, 0xe2, 0x2e, 0x82, 0x66, 0xca, 0x60, 0xc0, 0x29, 0x23, 0xab, 0x0d, 0x53, 0x4e, 0x6f},
	{0xd5, 0xdb, 0x37, 0x45, 0xde, 0xfd, 0x8e, 0x2f, 0x03, 0xff, 0x6a, 0x72, 0x6d, 0x6c, 0x5b, 0x51},
	{0x8d, 0x1b, 0xaf, 0x92, 0xbb, 0xdd, 0xbc, 0x7f, 0x11, 0xd9, 0x5c, 0x41, 0x1f, 0x10, 0x5a, 0xd8},
	{0x0a, 0xc1, 0x31, 0x88, 0xa5, 0xcd, 0x7b, 0xbd, 0x2d, 0x74, 0xd0, 0x12, 0xb8, 0xe5, 0xb4, 0xb0},
	{0x89, 0x69, 0x97, 0x4a, 0x0c, 0x96, 0x77, 0x7e, 0x65, 0xb9, 0xf1, 0x09, 0xc5, 0x6e, 0xc6, 0x84},
	{0x18, 0xf0, 0x7d, 0xec, 0x3a, 0xdc, 0x4d, 0x20, 0x79, 0xee, 0x5f, 0x3e, 0xd7, 0xcb, 0x39, 0x48},
}

// DecryptSM4ToString 解密SM4，返回一个string类型
func DecryptSM4ToString(text string, key string) string {
	if len(text) == 0 || len(key) == 0 {
		return ""
	}
	cipher, err := hex.DecodeString(text)
	if err != nil {
		return ""
	}
	paddingKey := PKCS7Padding([]byte(key), 16)
	return string(DecryptSM4(ByteToUint32(cipher), ByteToUint32(paddingKey)[:4]))
}

// DecryptSM4 SM4的解密函数
// 为了节省内存会改变参数text的值
func DecryptSM4(text []uint32, key []uint32) []byte {
	if text == nil || key == nil || len(text) == 0 {
		return nil
	}
	message := text
	RK := extendKey(key)
	for each := 0; each < len(text); each += 4 {
		message[each], message[each+1], message[each+2], message[each+3] =
			message[each+3], message[each+2], message[each+1], message[each]
		for step := 31; step >= 0; step-- {
			tmp := reverseEverRound(message[each:each+4], RK[step])
			message[each+3] = message[each+2]
			message[each+2] = message[each+1]
			message[each+1] = message[each]
			message[each] = tmp
		}
	}
	// 由于加密时对明文进行了补位，解密时需要去掉补位值
	res := toByteSlice(message)
	paddingNum := int(res[len(res)-1])
	return res[:len(res)-paddingNum]
}

// CryptoSM4ToString SM4的进一步封装
// 参数 message: 明文
// 参数 key: 密钥
func CryptoSM4ToString(message string, key string) string {
	if len(message) == 0 || len(key) == 0 {
		return ""
	}
	paddingMsg := PKCS7Padding([]byte(message), 16)
	paddingKey := PKCS7Padding([]byte(key), 16)
	return hex.EncodeToString(SM4(ByteToUint32(paddingMsg), ByteToUint32(paddingKey)[:4]))
}

// SM4 SM4加密算法的实现
// 为了节省内存，该函数会改变参数message的值
// 保留参数message的值请使用CryptoSM4ToString函数
func SM4(message []uint32, key []uint32) []byte {
	// 为了节省内存，以下过程会直接修改message的值
	if message == nil || key == nil {
		return nil
	}
	ciphertext := message
	RK := extendKey(key)
	for each := 0; each < len(message); each += 4 {
		for step := 0; step < 32; step++ {
			tmp := everRound(ciphertext[each:each+4], RK[step])
			ciphertext[each] = ciphertext[each+1]
			ciphertext[each+1] = ciphertext[each+2]
			ciphertext[each+2] = ciphertext[each+3]
			ciphertext[each+3] = tmp
		}
		ciphertext[each], ciphertext[each+1], ciphertext[each+2], ciphertext[each+3] =
			ciphertext[each+3], ciphertext[each+2], ciphertext[each+1], ciphertext[each]
	}

	return toByteSlice(ciphertext)
}

// everRound 轮函数，用于每轮加密
func everRound(inputBlock []uint32, rk uint32) uint32 {
	return inputBlock[0] ^ T(inputBlock[1:], rk)
}

// reverseEverRound 用于解密的轮函数
func reverseEverRound(inputBlock []uint32, rk uint32) uint32 {
	return inputBlock[3] ^ T(inputBlock[:3], rk)
}

// extendKey 密钥扩展算法
// 密钥扩展时不改变原始密钥（传入的密钥）
func extendKey(key []uint32) []uint32 {
	var rk uint32
	MK := make([]uint32, len(key))
	copy(MK, key)
	for i := 0; i < 4; i++ {
		MK[i] = MK[i] ^ FK[i]
	}
	for i := 0; i < 32; i++ {
		rk = MK[i] ^ TDet(MK, i)
		MK = append(MK, rk)
	}
	return MK[4:]
}

// TDet 用于密钥扩展算法的合成置换
// 相比于T函数，线性映射部分发生了变化
func TDet(num []uint32, i int) uint32 {
	block := num[i+1] ^ num[i+2] ^ num[i+3] ^ CK[i]
	block = NonlinearTrans(block)
	return block ^ CycleShiftLeft(block, 13) ^ CycleShiftLeft(block, 23)
}

// T 合成置换,用于轮函数
func T(inputBlock []uint32, rk uint32) uint32 {
	block := inputBlock[0] ^ inputBlock[1] ^ inputBlock[2] ^ rk
	// return LinearTrans(NonlinearTrans(block))
	return LinearTrans(NonlinearTransImpro(block))
}

// NonlinearTrans S盒映射，非线性变换
func NonlinearTrans(num uint32) uint32 {
	//numSlice := uint32ToUint8(num)
	//for i := 0; i < 4; i++ {
	//	numSlice[i] = SboxSm4[numSlice[i]>>4][numSlice[i] & 0x0F]
	//}
	//return binary.BigEndian.Uint32(numSlice)
	numSlice := uint32ToUint8(num)
	res := make([]uint32, 4)
	for i := 0; i < 4; i++ {
		res[i] = SboxSm4[numSlice[i]>>4][numSlice[i]&0x0F]
	}
	return res[0]<<24 | res[1]<<16 | res[2]<<8 | res[3]
}

// NonlinearTransImpro 改进的非线性映射函数
func NonlinearTransImpro(num uint32) uint32 {
	points := []uint32{
		(num & 0xF0000000) >> 28, (num & 0x0F000000) >> 24, (num & 0x00F00000) >> 20, (num & 0x000F0000) >> 16,
		(num & 0x0000F000) >> 12, (num & 0x00000F00) >> 8, (num & 0x000000F0) >> 4, num & 0x0000000F,
	}
	res := [4]uint32{}
	res[0] = SboxSm4[points[0]][points[1]]
	res[1] = SboxSm4[points[2]][points[3]]
	res[2] = SboxSm4[points[4]][points[5]]
	res[3] = SboxSm4[points[6]][points[7]]
	// return uint32(res[0]) << 24 | uint32(res[1]) << 16 | uint32(res[2]) << 8 | uint32(res[3])
	return res[0]<<24 | res[1]<<16 | res[2]<<8 | res[3]
}

// LinearTrans 线性映射变换
func LinearTrans(num uint32) uint32 {
	return num ^ CycleShiftLeft(num, 2) ^ CycleShiftLeft(num, 10) ^
		CycleShiftLeft(num, 18) ^ CycleShiftLeft(num, 24)
}
